


Shameless One-Shots of Gaster and You

by SuckMyBone_R18



Category: Undertale (Video Game)
Genre: Different versions of Gaster, During the War, F/M, Fluff, Forbidden Love, Gaster Blaster in my Asster, Hurt/Comfort, I accept all Gasters, Love, M/M, Multi, My friend saw this and I'm extremely traumatized, Other, Smut, before the war, help me, pre-game
Language: English
Status: In-Progress
Published: 2017-05-18
Updated: 2017-06-22
Packaged: 2018-10-30 03:44:11
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 3
Words: 4,030
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/10868376
Author URL: https://archiveofourown.org/users/SuckMyBone_R18/pseuds/SuckMyBone_R18
Summary: I have way too many smutty ideas of Gaster to keep them in my head. And so, I have spawned this horrific fic.





	1. Chapter 1

Heya, I guess this is where you can leave requests?  
I mean I got a lot of my own ideas, but hearing somebody else's would be neat.  
Besides I'm going to run low on creative ideas at some point it's best to get some now.

...

...

. . .

I might do fluff and comfort/hurt stuff instead of just smut and probably some weird things with other characters, but the smut will most definitely be centered around Gaster and different versions of him.

The fourth chapter is taking some time, I had to do it four fucking times so I'm not really excited about writing it a fifth time.


	2. Soldier!Gaster x Lost!Reader - I'll keep you safe...*

**Summary for the Chapter:**

> You're a simple villager, lost at the wrong place at the wrong time.  
> Though a monster has agreed to keep you safe.  
> After so many days you two have grown close, you two have to run to a different hiding spot every now and again so neither of you is harmed.  
> Though when it appears there is nowhere else to run and hide, Gaster wants to show you just how much he loves you.

You and Gaster sat in the bedroom of an old cottage, he was at the edge of the bed, only wearing cloth pants as he washes his body with a wet cloth. You had already bathed, wearing your dress as you stare at him, a light blush on your cheeks. He was a very big monster, tall, muscular... and you were a small human, watching him and getting awfully aroused by the sight of him. He was a very intimidating and honestly frightening monster. But after so long all you can think of him is a very handsome one... you two had just gotten here a day or two ago. You don't really keep track.

That's when he heaved a heavy sigh and you snapped out of your trance, noticing he had stopped cleaning his black magical flesh that was covered in scars and wounds. Though when you realized he also wasn't finished cleaning, you scooted closer.

"Gaster?" You whispered softly to him, he turned, a frown was on his face. You frowned as well, not sure what was wrong.

"Sweetheart..." You knew that tone, your eyes darkened with fear and sadness, that tone he used when he was near hopeless and defeated... but you two had run so far and for so long... what was making him give up now? "They... they've cut us off..." You gasped as he continued," we've got nowhere to run now... a-and they're closing in..." He sighed again, looking into your fearful eyes with his own depressed ones. "I'm going to keep you safe... we're not going to die... but... if this is the last time we see each other..." He swallowed as he turned around completely. "I want to make every moment feel amazing..." You were slightly confused as he picked you up and laid you down, your head on the pillows as he crawled over you, he smiled softly. "I want to make love to you.~" He purred. Your face went bright red.

"A-Ah G-Gaster... a-are you s-sure...?" He nodded, pulling your dress up, revealing your bra and panties which he went to remove as well. "O-Oh gosh y-you're serious..." He purred and hummed, looking over your now exposed body, his eyes full of adoration and love. He pulled his pants down and your eyes went wide. It was only reasonable a large monster had appropriately large proportions for every part of him... but wow... you were almost scared to have that inside. "I-It won't f-fit..." He hummed and nodded. "I know... but it doesn't need to." He went to press two fingers into you to stretch you, before pushing in a third, you moaning as he wiggled his fingers around inside of you. He pulled his fingers out after awhile, purring loudly still. "Are you ready for it?~" You gulped as he licked his fingers and hand clean, wiping his saliva on his cock to lube it. "I-I'm as ready as I c-can be.~" You watched as Gaster moved to press the tip against your pussy lips he rubbed the tip against your clit, making you jolt and gasp, whining softly as well. He then rubbed the tip between your pussy lips before he found your tiny virgin hole.

You let out a squeak when he entered, quickly going to grab at the pillows and sheets, making soft noises and groans as he continued to slowly press into you. He was grunting and panting softly himself, groaning and moaning as your tight pussy squeezed his cock. "A-Anngghh! S-Shit! T-Too tight!~" You tried to relax and loosen up some so it was easier for him to push in, but you found yourself tensing and clawing at the sheets with each small movement of his cock. "J-Just ram it in!" You squeaked, eager for his cock to just be inside. "A-Are you sure?" He asked and you whined. "P-Please!! Please ju-! AHH!~" You couldn't finish as he gave a harsh thrust to push what he could into you before the tip hit your cervix. You shivered and moaned, at the wonderful feeling of being stuffed full. "S-So f-full.~" "Your 'bout t-to get a lot f-fuller.~" He began to thrust in and out of you, holding onto your hips to keep you still. You moaned loudly, clawing at the bed harshly. "F-Fuck! Nnnghh!~ K-Keep squeezing me like that and y-you're gonna m-make me cum sooner!~" He went harder and faster as you let out soft cries, growing closer and closer to your orgasm, and it was obvious Gaster was close too as he grunted and growled and panted heavily his cock twitching and throbbing. You and Gaster cried each other's names in unison as the both of you came. Gaster's hot thick seed coating your cervix and your walls, starting to spill out of you due to the copious amount. The two of you were panting heavily, sweaty and smelled like sex... so much for that bath.

And that's when you heard them closing in... Gaster bent over and kissed you deeply and harshly before pulling away some. "I'm not going to leave you... I'll keep you safe... we're gonna be okay..." He nuzzled you... and you believed him. You weren't scared or worried... you kissed his cheekbones and his forehead, and head his skull close to you. "We're going to have a family... right?" He looked at you in surprise before chuckling deeply. "Of course we will...~" He pulled out of you. "Now rest my princess... I assure you, once you wake up all of this will be over..." You smiled sleepily and fell asleep as he began to dress again.

"I'll keep you safe... even at the cost of my own life..."


	3. Underfell!Dadster x Mother!Reader - Calm and Quiet

**Summary for the Chapter:**

> UF!Gaster needs you to keep him calm, controlled, and happy, and you need him for protection against other monsters.
> 
> ...And he needs you for other things.

**Notes for the Chapter:**

> I decided to make multiple things before the actual smut because I love UF!Dadster. The worst and best dad.  
> Also, I hope it makes up for me disappearing off the face of the Earth.

Light flooded the bedroom, making you whine and wake up, looking up you notice there was a shape blocking the light, a large shape that you immediately recognized, making you jolt up, your arms flying out in an invitation to the familiar monster. He closed the door, sighing and crawling onto the bed, he wrapped his arms around you and you wrapped your arms around him, smiling and humming. "Are you okay?" You asked as he leaned and relaxed into you. His red sweater startlingly against the black and white room that the two of you shared. His sweater and eyes were practically the only things that had color in the room, besides your own eyes, hair, and skin.

"No." His cold, hard, and cynical voice said the word so harshly anybody who didn't know him would probably flinch, you did when the both of you first started actually talking and being somewhat nice to each other. But you didn't flinch now, just rubbed his arm. "What do you need me to do?" He leaned back, putting a hand in your hair. "Take care of your goddamn kids." He hissed, pointing at the door. So  _that's_ what he was doing. Being a dad for once, that's a surprise. You got pregnant during one of his 'experiments' and now you had twin hybrid devil children that seemed to want to drink your blood and feast on your pain. And you were always the only one taking care of them until now it seemed. "I don't believe it..." "Don't believe what?" He spat harshly as you stared at him in wonder. "You were taking care of-" "NO I WAS NOT!" He shrieked his cheekbones bright red. "Don't deny it! You love-" "DON'T SAY THAT WORD!" He huffed and you hissed as he tugged on your hair, you just managed to see a flash of panic on his face before he let go of you, got off the bed and stormed out of the bedroom, you rubbed the back of your head, wincing. "Asshole." You huffed and got up, going to grab clean clothes and heading to the bathroom.

 

* * *

 

When you stepped into the nursery you stifled a gasp at seeing the doctor, his form looming over Script's crib, Astor screaming in the other one. He didn't look up, but he acknowledged your presence by saying,"Every damn time I try to calm one of them down the other starts screeching like a banshee." He sighed angrily, his red gaze flicking over to Astor briefly. "I thought he'd be my favorite son. I was completely wrong." You couldn't stifle your chuckle as you walked over to Astor's crib, upon seeing you he calmed down some, but still cried, whining and flailing still. "You shouldn't be playing favorites in the first place G." You looked up and locked your gaze with his confused one. "Why not? It worked with Papyrus and Sans." You frowned immediately at the mention of the two brothers, you looked down at Astor and then over at Script. You frowned worse. "What's wrong?" You flinched when Gaster touched your arm, leaning over Script's crib and the space between the two cribs. "Gaster... I want Astor and Script to be uh... no offense but... less like you, Sans, Papyrus, Undyne... everybody basically... I don't want these little guys turning into another Papyrus and Sans." You said looking into the red lights in his eye sockets, they flickered into whiteness, they rarely did and they normally did when he was relaxed or when he was just enjoying time with you, so at least you knew he wasn't mad.

"Well, I want at least one of them to be _somewhat_ like me. I am gonna homeschool these babies." You giggled a bit, "Of course Gaster, you can make them geniuses." You smiled at him and he smiled back, you leaned over Astor reaching to put a hand on Gaster's cheekbone as you kissed him, gently at first, but Gaster quickly got impatient pressing his teeth harder against your lips and pushing roughly at your lips with his tongue, you quickly pulled away, making him growl. "Calm your tits G. You want me to take of these babies right? I can't if you're gonna make out with me." You turned your attention back to Astor, picking him up and pulling him close to your chest. "You said once before that you prefer my rough make-out sessions that make your lips bleed to breastfeeding 'our little demons'," he air quoted you, going back to wiggling his fingers at Script.

You snorted. "Yeah because they bite my tits and it hurts like all hell." "And my bites don't?" He had an odd growl to his voice, suddenly he was glaring at the baby. And you realized that he thought the baby was  _challenging_ him. You almost wanted to burst into laughter, but Gaster looked so serious you forced any giggles down. "Oh they hurt, the babies just hurt worse because it's my _tits_ they're biting not my lips." He smirked, he looked pleased to hear that, as if the reassurance he hurt you more than the babies hurt you was just that great. But that's just how it was with Gaster, he was a sadist, clawing and biting and spitting insults during sex. It wasn't a surprise he was still a sadist out of sex, wanting to prove that he caused you the most pain, whatever type of pain it may be. That was the one thing you and Gaster were odd with, he wants to inflict emotional pain on you, but you want to know 100% that he loves you and cares for you. That's actually the one thing you had asked in return for being his little plaything, he struggled with agreeing because he wasn't sure  _how_ to prove he loves you and wants to protect you and make sure your okay. 

But he eventually learned what was too painful and what wasn't enough comfort. You turned away from Gaster bouncing Astor lightly, he immediately whined loudly, definitely not liking the bouncing. You stopped bouncing him, sighed and turned back to Gaster. "Can you make me a bottle?" He blinked, then nodded, stood and walked to the other side of the room where he kept all the other baby stuff. You knew, even if he tried to deny it, that he was trying to be a good dad.

 

* * *

 

What you expected to find in the bedroom, was just the normal bedroom, and maybe a half-naked Gaster sleeping. What you didn't expect to find was a half-naked Sans being shouted at by Papyrus. At first, when you saw them instincts screamed for you to run back to the nursery, back to your babies and a sleepy guard dog Gaster watching over them. You could probably scream for Gaster, but a little voice immediately asked. Why would he come? You tried to not let that little voice go on any longer, focusing back onto whatever the hell was going on. But none of what Papyrus was screaming about helped.

"What the  _fuck_ is going on?" You growled you've learned from Gaster how to intimidate monsters if you ever needed to. You always put on this sassy tough girl front in front of Sans and Papyrus, they actually think you're pretty cool.

"I'M TRYING TO GET SANS OFF OF YOUR CUM-STAINED BED!!" Papyrus shouted, Sans quickly responding with, "i don't see any cum stains though bro." "THAT DOESN'T MEAN THEY STILL HAVEN'T FUCKED ON IT!!" "everybody fucks on beds, everybody sleeps in beds afterward, what's wrong with wanting to take a goddamned nap?" You snorted and rolled your eyes. "Gaster does a shitty job of cleaning the sheets, so I'm not sure how clean that bed is Sans." You sighed. "I gave birth on it so-" Sans leaped off the bed instantly. "YOU WHAT?!?!" He screamed, going to wipe his hands on Papyrus who screeched. You couldn't hold back anymore, you burst into uproarious laughter, clutching your stomach as you dropped to your knees and then laid on the ground, gasping for air and laughing in between.

"Why is my mate gasping for air on the ground?"

Immediately the clamor going on with Sans and Papyrus stopped, you managed to catch your breath, confused. That's when you remembered Gaster was the second most feared monster in the underground, even his sons feared him. You shifted to sit, but Gaster was there to pick you up bridal style, him humming softly. "Are-" "They're asleep. Now, what do you two want?" He glared at his sons and they both swallowed both sweating. Sans finally answered. "u-uh I kinda got in t-trouble with the Snowdin dogs, and they t-threatened to rip me a-apart so I was hoping our great wonderful genius f-father could hide me?" Gaster just narrowed his eyes before tilting his head toward Papyrus. "So what are you doing here Pap?" Papyrus jolted at the nickname, but swallowed and answered obediently,"I came with Sans, to make sure the dogs didn't get to him on his way here!" He smiled nervously. Gaster then glanced down at you with a look that said,'what do you think?' You glanced over and sighed. "I don't know..." Immediately Sans and Papyrus became panicked. "I think we've both grown soft, G. We should help them." Sans let out a huge sigh of relief and Papyrus looked like he was about to collapse. 

"You know staying here isn't free though, right?" Gaster said as he carried you over to them. "You gotta watch over your bitty brothers." He pointed out the door. "Right across the hall, you better believe that's where you're sleeping too." He patted Papyrus's shoulder, his son immediately tensing up, but headed out Sans following, once they left Gaster locked the door with a bit of magic. "Now... let's continue from where he left off shall we?~" He let out a sultry purr, your face immediately flaring up as he tossed you onto the bed.

 

* * *

 

It's odd pressing lips to teeth, even if there was an invisible layer of magic to make it more comfortable. It was still odd, like kissing a wall, except hotter, and more comfortable seeing as there was something to wrap around. The other thing was, his teeth were sharp and he purposefully bit on your bottom lip and caught at it, tugging. He often smirked and growled as he did so. He was bent over you, tongue poking at the punctures and lapping up the blood, he had a taste for blood like your babies. He pulled away after a bit, purring and humming. "Would it be bad to say 'I love you'?" You snorted and kissed the edge of his mouth softly. "You can say it as long as you mean it." He chuckled. "I love you.~" He then pressed his mouth to your neck murmuring the three words over and over, you giggling. Then he bit lightly, you gasped, grabbing at his shoulders desperately, digging your nails in. He sucked on your neck, purring as you whined and bunched his sweater up in your hands. "G-Gasterrr." You panted as he pulled away, still holding onto his sweater. "I want to... do so many awful things to you.~" Gaster growled opening his mouth to press all his sharp teeth against your neck. "Nnnghh... G... As m-much as I would l-like for you to t-tear my throat out and all... maybe you'd w-want to... do s-something else?~" You smiled, rubbing Gaster's back, starting to pull his sweater up.

"Well seeing you naked would be quite the treat.~" He let you pull his sweater off, he straightened and smirked, showing off some of his sharp teeth and, though he wouldn't admit it, his muscles, scars and thumping soul. You immediately went to rub at his stomach and trail along his pants, grinning. He sighed and hummed. "Do like rubbing my muscles? Is it arousing?" You smacked his abs and he whimpered like an injured dog before snorting and bending to kiss you, you turned your head so he kissed your cheek, making him huff. "I know I made you angry, but I can't even kiss your lips?" You turned back to him and wrapped your arms around his neck pulling him in to kiss him deeply, yet still soft. He opened his mouth his tongue flicking at the small space between your lips, pressing a bit, trying to pry your lips apart. You opened your mouth allowing his slick, long, and odd tongue to slide past your lips, pressing at your tongue, enticing you to press back, which you did, your eyes fluttering close as you held him close, your arms around his neck your legs wrapping around his waist. You pulled him close enough to allow him to press his crotch against you, which was a mistake as he immediately began to hump and roll his hips into you making you moan into his mouth.

He pulled away from kissing you, saliva dripping from both of your mouths as you stared at each other dazed for a moment before you giggled and he smirked. He went to pull your shirt off, and you allowed him, your arms above your head. Gaster immediately threw your shirt across the room, his hands sneaking behind your back to undo your bra and of course, he treated that the same as your shirt. He then cupped your breasts in his hands with a goofy smirk. "Hot." You snorted. "What?" "Hot. You're hot.- No don't scrunch up your nose like that, it's a compliment." You laughed and patted his cheekbone. He kissed you as his hands went to your jeans, eagerly undoing the button and zipper.

And of course it was tossed away just like your shirt and bra, Gaster really did not care for your clothes, he didn't have reason to, he thought there were just in the way of the  _real_ fun. Even though that was the same fun that produced two satan-spawns, aka Astor and Script. You always told Gaster it was his fault you produced the demons, and after two weeks he finally admitted to his crimes. Now his pants and boxers and your panties were the clothes in the way, and Gaster's hands were already moving to your panties. You grabbed his wrists. "Take your pants off first." You purred, rolling up into his crotch before pulling away so he could take his pants off, he discarded his clothes with as much vigor as he discarded yours. You looked at the large bulge in his boxers and grinned looking back up at him. "You're excited.~" You remarked running a finger along the inside of his thigh, eliciting a shudder from him. "You're wet.~" He purred running a finger along your wetness to prove his point, you wiggling and whining as his phalange teased your wet pussy lips.

"Do you want me to take care of that?~" He growled pressing his bulge against your wet panties as he muttered into your ear. You wrapped your legs around his waist. "I'd love to see you try.~" You smirked, digging your nails into his shoulders as he immediately went to take your panties off tossing them, he immediately went to remove his boxers tossing them as well, revealing a slick tapered tentacle cock, wiggling around in arousal. Your hands twitched, eager to wrap around him, but he was already leading his cock to your wet entrance, you eagerly spread your legs and when the tip slipped inside you moaned and wrapped your legs around his waist. " _F-Fuccckk_.~" He chuckled. "You have one dirty mouth when you want to have one sweetheart.~" He kissed you as he continued to press into you, you continued to moan and he'd groan occasionally until finally, he settled deep in you. Gaster sighed in pleasure, starting to rock in and out of you, his cock sliding along your wet hot walls. You remembered when he first had sex with you and you knew then you were no longer a virgin, Gaster had practically taken your virginity and torn it to shreds, pounding you and leaving you unable to walk.

You now loved being pounded until you can't walk, and as Gaster sped up his thrusts and thrusted harder, you were sure he was gonna try and make you unable to walk again. You moaned louder and clawed at his shoulders more. " _G-Gahhhh...!~_ " You could barely speak, too enraptured by the pleasure, Gaster kissing and sucking along your neck wasn't helping either. Soon enough you could feel a hot knot start to form in your lower stomach, and it seemed Gaster wasn't too far behind, his cock twitching around inside. "Gaster! O-Oh _g-gaahhh!!~_ " His cock hit the special spot inside of you that made you cry out, the knot even tighter, it was almost painful. And soon enough you came, clawing at Gaster's shoulders as you cried his name loudly. You heard him grunt and then let out a low groan as cum filled your pussy, and you enjoyed every second. You could feel fluid under your nails and cover your fingers, you immediately pull your hands away from his shoulders and you saw bright red and void black covering your fingers. "Oh..." You blushed and showed him your blood-covered hands. He didn't look too surprised. He just chuckled and shrugged. "I've had worse." You immediately wondered what all has happened with him, but you didn't say anything, just sighed and kissed him, and he kissed back happily.

"I love you.~" He purred and you giggled, nuzzling his cheek before laying back. "Love ya too Gaster.~" He pulled out of you, laid down beside you and pulled you close. It didn't take long for you to fall asleep.

 


End file.
